C.S. Lewis's quote: "(The natural life) knows that if the spiritual life gets hold of it, all its self-centeredness and self-will are going to be killed and it is ready to fight tooth and nail to avoid that."
Following after the flesh is a dangerous way to live!
When the Bible talks about the flesh, it is referring to the cravings of the physical body and the soul, which is our mind, will and emotions. Our flesh tells us what we want, what we think, and how we feel - not what God wants, thinks and feels.
Romans 8:8 talks about catering to the flesh. Have you ever been to a catered party? You go and you sit down and there is a white table cloth and napkin, pretty China and silver. You can just order anything you want and get it. It is so much fun to just sit around and be catered to. When we cater to our flesh, it may feel good for a little while, but we are going to pay for it somewhere along the way.
The opposite of following after the flesh is following after God's Spirit. It says in the Bible in Galatians 5:16-17,"But I say, walk by the Spirit, and you will not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for they are opposed to each other, to keep you from doing the things you want to do."
In order to walk in the Spirit, every person has to be willing to go through a process, and it hurts. It hurts my flesh when I don't get my way. When God tells me to go to someone and say I'm sorry, when I don't think I did anything wrong to start with, when in fact I think they should apologize to me, but you do it because you love God and you do it because you believe it's His way. You need to understand that God will sometimes box you into a situation that is just so hard for you. Here is what I find that happens to me, God decides to deal with me on something on the inside, and if I'm not getting it, then he'll begin to bring a circumstance into my life to deal with me from the outside. The pressure on the inside and the pressure on the outside, crushes that flesh and God eventually gets His way. It all depends on how long it takes for me to submit to God's way.
Let the Lord Jesus Christ be as near to you as the clothes you wear.
Then you won't try to satisfy your selfish (fleshly) desires.